1. Field of the Invention
The present invention relates to an inspection apparatus, an exposure apparatus, and a method of manufacturing a device.
2. Description of the Related Art
In general, in a manufacturing process for ICs and LSIs, an exposure apparatus such as a stepper or a mask aligner transfers a circuit pattern formed on a reticle, a photomask, or the like onto a wafer coated with a resist.
In this transfer step, if a pattern defect or a foreign substance such as dust exists on a reticle or the like, the foreign substance is also transferred onto the wafer at the same time, resulting in a decrease in the yield of IC and LSI manufacture. In particular, when a reticle is used and circuit patterns are repeatedly exposed on many shot areas on a wafer by the step-and-repeat method, if a harmful foreign substance exists on the reticle, the foreign substance is exposed on the entire wafer surface. This greatly decreases the yield of ICs and LSIs.
Detecting the presence of a foreign substance on a reticle is therefore indispensable to a manufacturing process for ICs and LSIs. In general, a foreign substance inspection apparatus using the property of a foreign substance that isotropically scatters light is used.
For example, the surface of an object to be inspected is inspected by projecting a parallel beam onto the surface of the object from obliquely upward, and forming an image of a foreign substance on a one-dimensional image sensor (sensory array) by making the sensor receive scattered light from the foreign substance via a graded index microlens array (see Japanese Patent Laid-Open Nos. 7-43312 and 7-5115).
FIG. 10 shows the basic arrangement of an optical system of a foreign substance inspection apparatus disclosed in Japanese Patent Laid-Open Nos. 7-43312 and 7-5115. For simple explanation, only the optical system for inspecting a foreign substance on a blank surface of a reticle will be described below. In practice, however, this apparatus also includes an optical system for inspecting a foreign substance on a pellicle film that protects a circuit pattern surface of a reticle against foreign substances. Reference numeral 2 in FIG. 10 denotes a pellicle frame attached with a pellicle film.
A collimator lens 42 converts a laser beam which is emitted by a semiconductor laser 41 and has a divergence angle into a parallel beam. A λ/2 plate 43 then makes the polarization axis of the projected light parallel to a plane including the optical axis of the projected light and the optical axis of the light received by a light receiving unit 7. The laser beam is incident on the surface of an object to be inspected at an angle θ near parallel to the surface of the object. This forms a linear light projection area 5 by the laser beam on a blank surface 1a as a surface to be inspected.
If a foreign substance 3 exists on the light projection area 5, scattered light is generated by the foreign substance 3. An imaging lens 71 (lens array) which has lenses arrayed along the longitudinal direction of the light projection area 5 to receive scattered light focuses the scattered light on a line sensor 72. The imaging lens 71 is configured to form an image of the light projection area 5 on the line sensor 72. As denoted by reference symbol B in FIG. 10, this apparatus inspects foreign substances on the entire blank surface 1a by linearly scanning an overall optical system 10 in a direction perpendicular to the longitudinal direction of the light projection area 5 and parallel to the blank surface 1a, that is, the X direction.
There is also proposed an inspection apparatus which includes another light receiving unit 7′ having the same arrangement as that of the light receiving unit 7 in FIG. 10, and compares inspection maps from the two light receiving units to remove a false foreign substance signal generated when a light beam is scattered by a circuit pattern or the like, thereby accurately detecting the position and size of a foreign substance (see Japanese Patent Application No. 2008-108291 (U.S. patent application Ser. No. 12/424,468)).
FIG. 2 shows a technique of removing a false foreign substance signal. Reference symbol A in FIG. 2 denotes an example of the inspection map obtained from the light receiving unit 7; and B, an example of the inspection map obtained from the light receiving unit 7′. Since scattered light from a foreign substance commonly appears in both the inspection maps, it is possible to extract only a foreign substance signal by removing a signal appearing in only one of the inspection maps as a false foreign substance signal. Reference symbol C denotes an inspection map after the removal of false foreign substance signals from the two inspection maps A and B.
A basic management method for positions at which the foreign substance inspection apparatus starts inspection, that is, positions at which the light receiving unit starts scanning, will be described with reference to FIG. 4. Each scanning start position is managed by the distance from the origin switch position. The longitudinal direction of the line sensor is managed by the distance from a measurement end point of the line sensor. Since the origin switch and the line sensor have mounting errors, only a foreign substance within a predetermined range on a reticle placed in the foreign substance inspection apparatus is inspected by adjusting the scanning start position for each line sensor at the time of assembly of the foreign substance inspection apparatus.
A conventional technique of adjusting the scanning start positions of a plurality of light receiving units will be described. The conventional adjustment technique uses an adjustment ceramic plate (to be referred to as an “adjustment plate” hereinafter) on which predetermined patterns like the sign “+” are printed. This technique inspects the adjustment plate placed in the center of a stage in the foreign substance inspection apparatus, and adjusts the respective scanning start positions of a plurality of light receiving units such that the display position of a pattern image appearing in the obtained inspection map is located in the center of the inspection area. However, the conventional adjustment technique can only obtain an adjustment accuracy of about 1 mm at best.
FIG. 3 shows an example of inspection maps obtained by the conventional technique which has adjusted the scanning start positions of a plurality of light receiving units by using an adjustment plate. Reference symbol A denotes the inspection map obtained from one light receiving unit 7; B, the inspection map obtained from the other light receiving unit 7′; and C, the inspection map obtained by removing the false foreign substance signal generated based on the inspection maps A and B.
Foreign substance signals are respectively detected in the inspection maps A and B. Assume that a signal appearing only in one of the inspection maps is removed as a false foreign substance signal. In this case, if the light receiving units detect a foreign substance at different positions as in the case of the inspection maps A and B, the foreign substance signal may be deleted in the inspection map C.
As described above, according to the conventional technique of adjusting scanning start positions by using an adjustment plate, since the accuracy of adjustment of scanning start positions is insufficient, even a foreign substance signal may be deleted in the process of removing a false foreign substance signal by using a plurality of light receiving units.